Building a 48v Electric Dirtbike - Need help

My wife was wanting a project to work on and suggested an electric dirtbike from scrap parts.

We have found a frame at the local scrapyard for $100 and 2 Optima yellow top batteries (2nd hand)

I am planning on a chain driven direct drive bike. The main goal is for it to have a LOT of low end torque for fun off road. Top speed of 60km/h would be fine, a range of even 20km would be fine as well.

I am thinking of a brushless motor so I don't have to worry about brushes to replace. Here are some of the motors I am considering:

Keeping in mind that I've never done this sort of thing, a few suggestions anyway:

* Get rid of the exhaust system. ;-) If that tank is plastic, convert it into a weatherproof housing for the controller and other miscellaneous electronics. If it's steel, lose it as well.

* Direct drive is great for applications where you don't need much speed, but you may find that the best gearing for torque will produce a top speed of only 30kph or so, or even less. If you can find some way to use the existing gearbox and wet clutch you will end up with a bike that runs strong OR fast, and increments in between. You can also get that result if you can find a torque converter setup from a snowmobile or scooter, and adjust it for maximum torque. Both are much more work than direct drive, but if you succeed you will be less likely to want to immediately build something better.

* You have acquired two batteries, and need four. I think you may find it hard to match the batteries well enough to come up with a pack that will last. Even using two new batteries of the same brand and model may be problematic if the old ones are significantly sulfated. A mismatched pack will probably be fine for testing your conversion, but at some point, if you like the bike, plan on buying four new batteries.

looking at that bike again, I'm thinking it will be VERY hard to get four batteries of the size you probably have into it, plus a motor. You may have to choose between a 24 volt bike and using four smaller batteries.

Today my wife and I started stripping the bike. In just 2 hours we managed to strip the bike of all the petrol stuff.

Here is the bike total stripped. I may need to change the front section of the frame to fit in more batteries but so far it looks to easily hold 4 optima batteries. That may change once the motor is mounted.

Curious what size yellow tops you have? Two 75/25's can potentially carry our (very efficient) streamliners 55+ miles on one charge, at 55mph. With equivalent power, we've hit 80+mph top speeds. But those are best case scenarios i.e. no hills, straight, with properly treated (& heated) batteries, no trans, a smaller chain drive on a much lower drag machine. As said in different words above, the trade off is torque. If you stick with 24V, you "can" trade the top speed/range off for torque, and I suggest a high current (400A or more) controller too. & keep an eye on motor temp if you go there. We have new & used parts at destinyparts.com, like real Etek motors at the moment..., and a lot of full sized EV stuff that isn't listed. Just ask if you need something odd-ball that isn't found in a search. Have fun!

Here are some photos of the 2 yellowtop batteries I got for nothing at the scrapyard. One measures 12.21v, the other reads 11.97v. I haven't charged them yet but as a "scrapyard" bike, I'll use any battery to start with. I've even asked CHL Battery if he has any 50Ah cells he would like to donate in return for some advertising in the form of youtube and other video websites. I doubt it but it's worth a try because I'd really like to run CHL cells on this at 6C (300 Amps) to see how they handle.

I suggest you charge those batteries ASAP, and don't be surprised if at least one of them proves to be unusable. Lead-acid batteries, even deep-cycle ones (these look to be 'compromise batteries' that provide both starting amps and *somewhat* deeper discharge) are damaged by sitting around with less than about 60% charge.

If you are going with direct drive (and probably even if you aren't), my guess is you want to put the motor in the space just under and partially behind the seat, higher up than the heavier batteries. Most conversions like this modify at least part of the frame to hold the batteries - just try to keep them as low as possible, as a dirt bike with a high CG (center of gravity) will be constantly trying to fall, and will frequently succeed.

Good, you have the bigger size. Like leftiebiker said, you'll want to get all you can from them, so get them on a charger right away. Top them off once a week, or just keep a trickle charger on them when not in use.

I converted a Porsche 914 from lead acid to Li using 102 100Ah CALB cells. Check it out at www.shiftev.com if you want. I'm a CALB dealer too. Can't give them away, but have good pricing.

Are you familiar with the "search" feature on www.evalbum.com? If not, save a lot of time and money by learning from others... The search feature is a little tricky to find and use, but once I did, it has been invaluable finding comparable projects.

My wife and I have decided to do things right. This means installing a Motenergy ME0708 motor with 16 x CHL 50Ah LiFePo4 cells to make a 48v pack, all coupled with an Alltrax controller. My wife even said to me last night "Why don't we run 72v?". This would mean a bigger motor (ME0709), bigger controller and 8 more CHL cells. Here's the summary so far:

Is this your first conversion? If so, I strongly advise against going all-out with it. This is especially true because it's a dirt bike. Unless you plan to also convert it for road use only, you don't want to spend all that time and money, only to find out that it's either unrideable, or have it fall and smash expensive components. Your original idea is probably best, with a modification: build a cheap 24 to 48 volt bike, but try to do it so you can upgrade the batteries, and maybe the motor and controller. A 60 volt motor should be more than enough, though, and it will run on 48 volts or even 36 if you choose it with that in mind.

Again, Leftie has a good point. This is probably tuff to accept if you're mind is already going there. I know how that is! But unless you have an abundance of design time, don't want to ride it soon, and a healthy budget that leaves room for oversights and improvements - keep it simple. Have you confirmed your current motorcycle is adequate to fit a 72V Li version described above? (safely). Physical fit, as well as shocks for the added weight, brakes, CG, etc.,. Your description didn't mention a Li BMS or charger. You'll get a quick EV grin out of building a lead acid machine (or a lower voltage Li) with what you have already started. Then, build on that success by selling it or graduating some components to a more complex machine. These suggestions are not to hold you back, but to prevent, or at least warn you about the burnout some folks go through.

Thanks for the heads up guys. I've converted 3 bikes previously, all lithium, 2 hubs and one chain driven. However they were all push bikes. This is my first motorbike frame. I'm just doing this project on the side so it won't be done for 6 months or more. Maybe I should be a little clearer. I'm going to buy the parts one at a time, first the motor and sprockets and chain. Then controller. Then run the bike on the lead acid batteries from the scrapyard. I now have 4 car batteries all holding a good charge (for how long I don't know). As for the budget, as it's over months, cash shouldn't be a problem. I've got a jar marked "petrol" in my drawer. Every payday I put in $100 pretending that's how much it would have cost in fuel if I didn't have my electric scooter. It's already over $450. I've talked with my supplier and if I buy a 48v CHL pack then it will come with a BMS.

My wife and I have decided to stick with 48v lithium pack because of the frame size. We want to keep everything inside the frame if possible. We are opting for an external charger for the lithium pack. The shocks and brakes are in great condition. The bike has a new set of pads, either that or no one rode it much, there's over 9mm of pad! Super strong grip too. Suspension is soft and effective with no leaks anywhere.

I see the only difficult part of the project is mounting the motor, fitting a drive sprocket and lining up the chain. I've got lots of good design tips off evalbum on how to hold the batteries in place. I've just scored 12m of 600A hard core battery cables and 10m of 800A flexible battery cable. My work just replaced the UPS battery bank for the building, a 240v bank made up of huge 2v cells waist high! So that saves me trying to find cable that won't melt under 100A (300A peak).

Price blowouts are certain to happen, I know this and its why we are not in a hurry to get the bike going. Just taking it nice and slow. Some people take up knitting, we wanted to put our skills into making something fun.

That sounds like a pretty good plan. Still, of you want to ride the bike off-road, make sure the batteries and controller are well protected, from crashes, from mud, from water... You might want to consider a plastic battery case behind aluminum crash plates, with a vent hose leading from it to a high spot on the bike, and a little blower sending in cooling air, again from high up on the frame. Either that or try to find batteries that are sturdy and have weatherproof connections.

We have ordered the MARS ME0708 motor and I've worked out how to mount the motor. Just to clarify, when I say off-road, I really mean a friends farm paddock and a couple of dirt tracks, and if it's raining we won't be riding it, but I DO like the idea of crash plates to protect the batteries. I'll be using steel angle to sit the batteries and strap them in, then build a box around the cells (basically).

Well if ANYONE is thinking of ordering ANYTHING from EV-WORKS in Western Australia....DON'T!!!!!!

I have paid for my MARS ME0708 motor from EV Works well over a week ago and have not even had an email saying he has received my money or anything. The company is next to IMPOSSIBLE to contact, their mobile phone number 0447 799 741 is switched off 99.99% of the time and they never reply to any emails.

I was considering buying a motor, speed controller and contactor from this company but after this, NO WAY!

Wow, this forum works better than phone calls. About half an hour after posting I got a call from EV Works saying they posted it 6 days ago. What happened to email updates?? Ah well. At least it's in the mail.

In the Middle Ages we had the pillory, nowadays we have the Internet and VisforVoltage :-)

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My rides:
QvR vR one: a Swiss package of pure understatement - innocent and to some eyes (from some angles) exceedingly ugly looks, but with raw and hardly containable electron power up to real 95 to 100km/h! And a literally rock-hard suspension due to a carrying capacity of twice it's unladen weight... Now converted to more controllable and efficient brushless motor and vector-contoller.

E-Sprit Fury (basis is the Erider Thunder 5000) since May 03, 2011. Highly moded - but now in active retirement

Any particular reason this discussion has hijacked this topic, rather than occurring in the topic where it belongs...? It may seem like harmless topic drift now, but just try to find this information here 6 months from now...

After some phone calls....I have the motor. Let me say this, it is a LOT bigger than I thought it would be and 14kg is a lot for a motor. It's the biggest motor I've ever used on a bike! At least we now have a motor and can get to work on designing how to mount it.

I have been slack not updating this forum but heres a big update. After getting the #530 chain from the USA I found the red sprocket was not cut correctly and I had to order a professionally cut sprocket from "electric motorsport". Anyway so I ordered a 72 tooth sprocket and gave them all the measurements and waiting for it to be posted.

I ended up welding some battery trays together onto the bike, 2 down low and 2 up high. I was really contrained with space, I may move the batteries depending on how it handles. All 16 cells now fit in their trays.

I borrowed a 9 tonne electric hydraulic crimping tool to crimp the connectors onto the fat wire. This thing makes EASY work of the cimping process, just hold the trigger and hold the lug in place for 5 seconds while it crimps it.

I got to wire everything up and program the controller and found I had a hall sensor throttle, not a 0-5k as required so I used a 0-5k pot as a temporary testing device. Once again, onto electric motorsport to order a magura 0-5k twist throttle. With the 0-5k pot I was able to do my first power up! I had limited the power to 200 battery Amps. The cycle analyst is still coming so I don't know how much power it used in this video but I'd say maybe around 20-50Amp because there was no load. I LOVE the sound!!!

I have found a manufacturer of BMS for electricmotorcycle. The website is http://www.acrel-ms.cn you can contact by email dgl@acrel-ms.cn
They designed 16S-24S BMS for emotorcycle with lifepo4 battery pack, 48V-76.8V system. 16S BMS has active balance mode. It is really a good
BMS for Motorcycle with cell information(voltage,current,temperature..) dislayed all the time.